Substrate holding apparatus

ABSTRACT

A substrate holding apparatus for holding substrates in vertical posture includes a first holder, a second holder and a substrate fall preventing stand arranged along edges of the substrates and located below centers of the substrates. The first holder is disposed in a position for holding the substrates between lower ends and lateral ends of the substrates. The second holder is disposed in a position for holding the substrates at the lower ends of the substrates, or in a position opposed to the first holder across the lower ends for holding the substrates between the lower ends and lateral ends of the substrates. The substrate fall preventing stand being disposed opposite the first holder across the lower ends of the substrates and above the second holder.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] This invention relates to a substrate holding apparatus for holding substantially circular substrates such as semiconductor wafers.

[0003] (2) Description of the Related Art

[0004] A conventional example of such apparatus is shown in FIG. 1. FIG. 1 is a front view showing a principal portion of a substrate holding apparatus known in the art.

[0005] The apparatus includes a first holder 101 and a second holder 102 for holding wafers W in positions between lower ends and lateral ends thereof. These holders 101 and 102 are in contact with edges of the wafers W. Further, a fall preventing stand 103 is disposed between the holders 101 and 102 for preventing the wafers W from falling in a direction perpendicular to the plane of FIG. 1. The stand 103 is out of contact with the wafers W.

[0006] This substrate holding apparatus is immersed with the wafers W in a treating solution stored in a treating tub, for example. After a predetermined time of treatment, the treating solution is replaced by deionized water for cleaning treatment.

[0007] The conventional apparatus with the above construction has the following drawback.

[0008] When the conventional substrate holding apparatus is used in treating the wafers W in an etching or cleaning process, for example, the wafers W undergo stress which could damage circuits such as LSIs formed on the wafers W. Thus, the treatment of wafers W by using the conventional substrate holding apparatus may result in a reduced yield.

SUMMARY OF THE INVENTION

[0009] This invention has been made having regard to the state of the art noted above, and its object is to provide a substrate holding apparatus that can relieve the stress applied to substrates, thereby avoiding a reduced yield.

[0010] The above object is fulfilled, according to this invention, by a substrate holding apparatus for holding substrates in vertical posture, comprising a first holder, a second holder and a substrate fall preventing stand arranged along edges of the substrates and located below centers of the substrates, the first holder being disposed in a position for holding the substrates between lower ends and lateral ends of the substrates, the second holder being disposed in a position for holding the substrates at the lower ends of the substrates, or in a position opposed to the first holder across the lower ends for holding the substrates between the lower ends and lateral ends of the substrates, the substrate fall preventing stand being disposed opposite the first holder across the lower ends of the substrates and above the second holder.

[0011] The first holder, second holder and substrate fall preventing stand are located below the centers of the substrates. Further, the first holder contacting edges of the substrates is disposed between the lower ends and lateral ends of the substrates. The second holder contacting edges of the substrates is disposed at the lower ends of the substrates, or in a position opposed to the first holder across the lower ends of the substrates. Thus, the first holder and second holder have a shorter spacing therebetween circumferentially of the substrates than in the prior art. As a result, stress on the substrates resulting from expansion and contraction of the substrates may be lessened to reduce adverse influences on the circuits and the like formed on the substrates, and avoid the lowering of yield.

[0012] If the first or second holder or the fall preventing stand were located above the centers of the substrates, a treating solution could flow down to form stains on the substrates when the substrates are pulled up out of the treating solution. The above construction is effective to avoid such an inconvenience since the first or second holder or the fall preventing stand is not located above the centers of substrates.

[0013] Preferably, the first holder and second holder are arranged such that a straight line extending through a point of contact between an edge of each substrate and the first holder and a point of contact between an edge of the substrate and the second holder and a tangent to the substrate in the second holder form an angle in a range of 25 to 40 degrees outwardly of the substrate.

[0014] Where a straight line extending through the point of contact between an edge of each substrate and the first holder and the point of contact between an edge of the substrate and the second holder and a tangent to the substrate in the second holder form an angle in a range of 25 to 40 degrees outwardly of the substrate, friction occurring at the edges of the substrates in the first and second holders in time of expansion or contraction of the substrates is smaller than in the prior art. This lessens the stress acting radially of the substrates.

[0015] An angle smaller than 25 degrees renders the holding of the substrates unstable. An angle larger than 40 degrees causes adverse influences of stress on the substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.

[0017]FIG. 1 is a fragmentary view in vertical section of a substrate holding apparatus known in the art;

[0018]FIG. 2 is a perspective view showing an outline of substrate treating equipment having a substrate holding apparatus according to this invention;

[0019]FIG. 3 is a perspective view showing an outline of the substrate holding apparatus according to the invention;

[0020]FIG. 4 is a fragmentary view in vertical section of the substrate holding apparatus;

[0021]FIG. 5 is a graph showing average values of frictional forces occurring at various angles; and

[0022]FIG. 6 is a fragmentary view in vertical section of a modified substrate holding apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A preferred embodiment of the invention will be described in detail hereinafter with reference to the drawings.

[0024]FIGS. 2 through 4 show one embodiment of this invention. FIG. 2 is a perspective view showing an outline of substrate treating equipment having a substrate holding apparatus according to this invention. FIG. 3 is a perspective view showing an outline of the substrate holding apparatus. FIG. 4 is a fragmentary view in vertical section of the substrate holding apparatus.

[0025] The substrate treating equipment having substrate holding apparatus 1 in this embodiment is exemplified by what is shown in FIG. 2. This substrate treating equipment is constructed for cleaning wafers W. A front panel 3 shown in a far end defines an opening 5 for loading and unloading wafers W. A plurality of treating units are arranged in a row opposite the wafer loading/unloading opening 5.

[0026] For example, a first cleaning unit 7 is disposed adjacent the end (left-hand side in FIG. 2) remote from the front panel 3, a second cleaning unit 9 is disposed next, and then a third cleaning unit 11. Each cleaning units 7, 9 or 11 includes a transport mechanism 7 a, 9 a or 11 a for moving a plurality of wafers W between its own treating tubs. Each transport mechanism 7 a, 9 a or 11 a is vertically and horizontally movable independently of the other transport mechanisms. A main transport mechanism 13 is disposed next to the third cleaning unit 11 for transporting one lot of wafers W to each of the cleaning units 7, 9 and 11.

[0027] Each transport mechanism 7 a, 9 a or 11 a has the substrate holding apparatus 1. As shown in FIG. 3, the substrate holding apparatus 1 is attached to a base member 15 of transport mechanism 7 a, 9 a or 11 a. The base member 15 is in the form of a plate sized for immersing the wafers W in each unit. The base member 15 has a first holder 17, a second holder 19 and a substrate fall preventing stand 21 attached thereto and arranged adjacent the treating tubs. These holders 17 and 19 and stand 21 are in the form of square bars and are fixed to one another at forward ends thereof by a connecting member 23.

[0028] As shown in FIG. 4, the first holder 17, second holder 19 and fall preventing stand 21 are arranged below the centers of wafers W. Each of the first holder 17 and second holder 19 defines a plurality of contact/support portions 17 a or 19 a in the form of grooves for contacting edges of wafers W. These contact/support portions 17 a or 19 a are arranged at predetermined intervals for holding a plurality of wafers W. The contact/support portions 17 a and 19 a have a groove width larger than the thickness of wafers W.

[0029] The contact/support portions 17 a have straight slopes extending rightward and downward for contacting and supporting the wafers W at obliquely downward edges thereof. The contact/support portions 19 a have substantially horizontal surfaces for contacting and supporting the wafers W at lower ends thereof. These slopes and surfaces may be arcuate surfaces facing upward.

[0030] The above contact/support portions 17 a and 19 a may be replaced by contact/support portions having a V-shaped cross section as seen from the edges of wafers W.

[0031] The substrate fall preventing stand 21 is disposed at the same height as the first holder 17 in the vertical direction of wafers W, and defines a plurality of fall preventing grooves 21 a arranged at the predetermined intervals for receiving and preventing fall of wafers W. The fall preventing grooves 21 a have slopes 21 b formed in positions out of contact with the edges of wafers W. The fall preventing grooves 21 a are smaller in width in plan view than the contact/support portions 17 a and 19 a and slightly larger than the wafers W. Side surfaces of the fall preventing grooves 21 a contact the front surfaces or back surfaces of wafers W to prevent fall of wafers W.

[0032] A first straight line L1 (two-dot chain line in FIG. 4) extending through a point of contact between the edge of wafer W and the first holder 17 and a point of contact between the edge of wafer W and the second holder 19, and a tangent L2 (dotted line in FIG. 4) to the wafer W in the second holder 19, form an angle A1 outwardly of the wafer W. This angle A1, preferably, is in a range of 25 to 40 degrees for the following reasons.

[0033] The graph in FIG. 5 shows variations in the average of static friction in the holders 17 and 19 derived from various angles A1 set for wafers W 200 mm in diameter (8 inch in diameter) and the wafers W 300 mm in diameter (12 inch in diameter). The variations are shown in ratios, with angle A1=52 degrees set for the wafers W 200 mm in diameter as a reference, and angle A1=52.5 degrees for the wafers W 300 mm in diameter as a reference.

[0034] As seen from this graph, the ratio decreases with the angle A1. That is, the smaller the angle A1 is, the smaller is the static friction in the first and second holders 17 and 19. Thus, stress acting on wafers W by expansion and contraction may be restrained.

[0035] The angle A1 has limits imposed by construction. An angle A1 smaller than 25 degrees renders the holding of wafers W unstable. An angle A1 larger than 40 degrees causes adverse influences of stress acting on wafers W. A preferred angle A1 is about 30 degrees. With this angle A1, wafers W may be held stably while diminishing stress. It is to be noted that an angle A2 in the conventional example shown in FIG. 1 is about 45 degrees or larger.

[0036] As noted hereinbefore, the first holder 17, second holder 19 and fall preventing stand 21 are located below the centers of wafers W. Further, the first holder 17 in contact with the edges of wafers W is disposed between the lower ends and lateral ends of wafers W. The second holder 19 in contact with the edges of wafers W is disposed at the lower ends of wafers W. Thus, the first holder 17 and second holder 19 have a shorter spacing therebetween circumferentially of wafers W than in the prior art, thereby reducing friction produced at the edges of wafers W. As a result, adverse influences of stress on the wafers W resulting from expansion and contraction of wafers W may be reduced to avoid the lowering of yield.

[0037] If the first or second holder 17 or 19 or the fall preventing stand 21 were located above the centers of wafers W, the treating solution could flow down to form stains on the wafers W when the wafers W are pulled up out of the treating solution. The construction according to the invention is effective to avoid such an inconvenience since the first or second holder 17 or 19 or the fall preventing stand 21 is not located above the centers of wafers W.

[0038] <Modification>

[0039] A modification will be described next with reference to FIG. 6. FIG. 6 is a fragmentary view in vertical section of a modified substrate holding apparatus.

[0040] In the foregoing embodiment, the first holder 17 and fall preventing stand 21 are arranged at the same height with respect to the wafers W. The second holder 19 is located at the lower ends of wafers W. However, this invention is not limited to the foregoing embodiment.

[0041] In the modification, the first holder 17 and second holder 19 are arranged in bilaterally symmetrical positions with respect to the lower ends of wafers W. The substrate fall preventing stand 21 is disposed above the second holder 19. Of course, the first holder 17, second holder 19 and fall preventing stand 21 are all arranged below the centers of wafers W.

[0042] A first straight line L1 (two-dot chain line in FIG. 6) extending through a point of contact between the edge of wafer W and the first holder 17 and a point of contact between the edge of wafer W and the second holder 19, and a tangent L2 (dotted line in FIG. 6) to the wafer W in the second holder 19, form an angle A1 outwardly of the wafer W. This angle A1, preferably, is in the range of 25 to 40 degrees for the reasons noted hereinbefore.

[0043] In the above embodiment and modification, the first holder 17, second holder 19 and fall preventing stand 21 are in the form of square bars. This invention is not limited to such a configuration, but may use bars of circular cross section instead.

[0044] The substrate holding apparatus according to this invention may be used also in various substrate treating equipment other than the substrate treating equipment constructed for substrate cleaning treatment.

[0045] This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention. 

What is claimed is:
 1. A substrate holding apparatus for holding substrates in vertical posture, comprising: a first holder, a second holder and a substrate fall preventing stand arranged along edges of the substrates and located below centers of the substrates; said first holder being disposed in a position for holding the substrates between lower ends and lateral ends of the substrates; said second holder being disposed in a position for holding the substrates at the lower ends of the substrates, or in a position opposed to said first holder across the lower ends for holding the substrates between the lower ends and lateral ends of the substrates; said substrate fall preventing stand being disposed opposite said first holder across the lower ends of the substrates and above said second holder.
 2. An apparatus as defined in claim 1, wherein said first holder and said second holder are arranged such that a straight line extending through a point of contact between an edge of each substrate and said first holder and a point of contact between an edge of said each substrate and said second holder and a tangent to said each substrate in said second holder form an angle in a range of 25 to 40 degrees outwardly of said each substrate.
 3. An apparatus as defined in claim 1, wherein said first holder and said substrate fall preventing stand are arranged vertically level with each other.
 4. An apparatus as defined in claim 2, wherein said first holder and said substrate fall preventing stand are arranged vertically level with each other.
 5. An apparatus as defined in claim 1, wherein said first holder, said second holder and said substrate fall preventing stand extend from a base of a transport mechanism, and have distal ends thereof fixed to one another by a connecting member.
 6. An apparatus as defined in claim 2, wherein said first holder, said second holder and said substrate fall preventing stand extend from a base of a transport mechanism, and have distal ends thereof fixed to one another by a connecting member.
 7. An apparatus as defined in claim 3, wherein said first holder, said second holder and said substrate fall preventing stand extend from a base of a transport mechanism, and have distal ends thereof fixed to one another by a connecting member.
 8. An apparatus as defined in claim 4, wherein said first holder, said second holder and said substrate fall preventing stand extend from a base of a transport mechanism, and have distal ends thereof fixed to one another by a connecting member.
 9. An apparatus as defined in claim 1, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 10. An apparatus as defined in claim 2, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 11. An apparatus as defined in claim 3, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 12. An apparatus as defined in claim 4, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 13. An apparatus as defined in claim 5, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 14. An apparatus as defined in claim 6, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 15. An apparatus as defined in claim 7, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 16. An apparatus as defined in claim 8, wherein said first holder and said second holder have groove-like contact/support portions formed in upper positions thereof.
 17. An apparatus as defined in claim 1, wherein said substrate fall preventing stand has slopes formed in positions out of contact with the edges of the substrates.
 18. An apparatus as defined in claim 2, wherein said substrate fall preventing stand has slopes formed in positions out of contact with the edges of the substrates.
 19. An apparatus as defined in claim 3, wherein said substrate fall preventing stand has slopes formed in positions out of contact with the edges of the substrates.
 20. An apparatus as defined in claim 1, wherein said second holder is disposed in a position symmetrical to said first holder with respect to the lower ends of the substrates. 